Contraceptive for male monkeys. Humans next?
A contraceptive gel provides long-term and reliable contraception in male rhesus monkeys. The product, Vasalgel™, tried on rabbits in 2016, has the potential to be a reversible alternative to vasectomy.
Vasalgel™ is a non-pharmaceutical hydrogel — a network of natural or synthetic polymer chains which are highly absorbent (absorbing over 90% water). Hydrogels also have flexibility very similar to natural tissue due to their significant water content. When injected into the vas deferens (the duct that conveys sperm from the testicle to the urethra) the gel fills the duct, forming a barrier to the movement of sperm.
This method of contraception could become an alternative to a vasectomy as it was able to prevent any conceptions occurring in a test group of 16 rhesus monkeys. The work was published in the open access journal Basic and Clinical Andrology.
"Our research shows that Vasalgel™ placement into the vas deferens produces reliable contraception in mature male rhesus monkeys — as shown by the lack of pregnancies in females housed with the males.
"Importantly, we show that the method of Vasalgel™ placement is safe and produced fewer complications than usually occur with a vasectomy."
Catherine VandeVoort PhD, Department of Obstetrics and Gynecology, California National Primate Research, University of California and lead author.
Dr VandeVoort adds: "Vasalgel™ shows real promise as an alternative to vasectomy because research in rabbits has previously shown the product to be reversible. Although it is possible to reverse a vasectomy, it is a technically challenging procedure and patients often have very low rates of fertility following reversal."
Researchers selected 16 adult male monkeys for surgery that involved injection of Vasalgel™ into their vas deferens. Monkeys were then monitored closely for 7 days for healthy recovery before being introduced back into their normal group housing. This consisted of large outdoor enclosures with between 10 to 30 monkeys that including male and female infants, juveniles and adults.
Each housing group had between one and three males who had been administered Vasalgel™. Males were housed with their groups for at least one breeding season of approximately six months, with no conceptions occurring. The expected pregnancy rate under similar circumstances is approximately 80% per breeding season.
One monkey out of the 16 that received Vasalgel™ showed signs of sperm granuloma (a hard build-up of sperm in the vas deferens) as a result of the injection. This is a common complication following a vasectomy, occurring in around 60% of cases in humans, according to the researchers.
Discomfort or serious side effects caused by lumps of fluid, sperm granulomas, collecting from the blood in sperm can appear along the vasa deferentia or epididymides in vasectomized men, but are rare following a vasectomy. But, researchers believe the typical rate of sperm granuloma in male rhesus monkeys undergoing vasectomy is around 15%.
Researchers say future research should investigate the reversibility of Vasalgel™ placement in rhesus monkeys in order to move forward as a potential alternative to vasectomy for human males.
Options for male contraception are limited. The purpose of this study was to use a nonhuman primate model to evaluate Vasalgel™, a high molecular weight polymer being developed as a contraceptive device for men.
Sixteen adult male rhesus monkeys received intravas injections of Vasalgel, consisting of 25% styrene maleic acid in dimethyl sulfoxide. After a one-week recovery, males were returned to outdoor group housing, which included at least 3 and up to 9 intact, breeding females with a successful reproductive history.
Treated males have had no conceptions since Vasalgel injections. All males were housed with intact females for at least one breeding season and seven have been almost continually housed with females for 2 years. Complications were minor and included one incident of incorrect placement of Vasalgel into the vas deferens and the development of a sperm granuloma in one animal. Three unilateral vasectomies were performed, one was necessary for incorrect placement of Vasalgel, the other two were elective.
Intravas injection of Vasalgel in sexually mature adult male rhesus monkeys was effective in preventing conception in a free-living, group environment. Complications were few and similar to those associated with traditional vasectomy.
Authors: Angela Colagross-Schouten, Marie-Josee Lemoy, Rebekah I. Keesler, Elaine Lissner and Catherine A. VandeVoort
Primate Macaca mulatta Hydrogel Vas deferens Styrene maleic acid polymer Fertility Vasectomy Vasalgel Contraception Sterilization Colony management
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